Packaging for surgical dressings and like medical applications needs to be of reliable high quality with a virtually guaranteed airtight seal whilst being easy to open rapidly, as required in an emergency situation. Packaging machines best suited for wrapping medical applications employ a four sided sealing technique whereby each product is deposited between two webs of packaging material which are sealed along the longitudinal edges of the product (those edges extending longitudinally of the production line) and transversely at each end of the product. Ease of opening of such packages is assisted by provision of gaps or "skips" in the longitudinal seals of each package beyond the end seals of the package. Ease of opening may be further enhanced by provision of a thumb notch in one of the webs of the packaging.
Validation of the process for packaging medical applications is essential and the complexity of the packaging process makes self-validation or autoregulation of such machines difficult. Quality control criteria are exceptionally high and quality control is time consuming when carried out by the standard technique of batch testing of the packaged products.
Seal integrity must be ensured. To achieve this through the design of the machine the conditions effecting seal integrity must be controlled within strict parameters. The pressure of compression together of the edges of the webs of material to be welded is one such condition that must be strictly controlled. The rate of package production and, where the welding is by heating of thermo plastic material, the temperature of the welding elements are two other such conditions.
In conventional horizontal flow four-sided seal packaging machines the longitudinal edges of the packages are sealed by co-acting pairs of vertically-spaced rollers which compress together to weld the webs of packaging material together. A respective set of such rollers is provided to weld the left hand and right hand longitudinal edges of the packages on the production line. The upper rollers for the right and left hand edges are generally interconnected by one axle shaft, while the lower rollers for the right and left hand edges are inter-connected by a further shaft. This arrangement and the manner by which the co-acting pairs of rollers are advanced and retracted relative to each other to adjust the pressure of compression presents considerable problems in reliably controlling the pressure of compression and, hence, seal integrity.
It is a general objective of the present invention to provide a four-sided seal packaging machine which is capable of reliably producing packages of high quality and high seal integrity.